/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.io;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Throwables;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Closeable;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.logging.Level;
import javax.annotation.Nullable;

/**
 * A {@link Closeable} that collects {@code Closeable} resources and closes them all when it is
 * {@linkplain #close closed}. This is intended to approximately emulate the behavior of Java 7's
 * <a href="http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html"
 * >try-with-resources</a> statement in JDK6-compatible code. Running on Java 7, code using this
 * should be approximately equivalent in behavior to the same code written with try-with-resources.
 * Running on Java 6, exceptions that cannot be thrown must be logged rather than being added to the
 * thrown exception as a suppressed exception.
 *
 * <p>
 * This class is intended to be used in the following pattern:
 *
 * <pre>
 * {
 *     &#64;code
 *     Closer closer = Closer.create();
 *     try {
 *         InputStream in = closer.register(openInputStream());
 *         OutputStream out = closer.register(openOutputStream());
 *         // do stuff
 *     } catch (Throwable e) {
 *         // ensure that any checked exception types other than IOException that could be thrown
 *         // are
 *         // provided here, e.g. throw closer.rethrow(e, CheckedException.class);
 *         throw closer.rethrow(e);
 *     } finally {
 *         closer.close();
 *     }
 * }
 * </pre>
 *
 * <p>
 * Note that this try-catch-finally block is not equivalent to a try-catch-finally block using
 * try-with-resources. To get the equivalent of that, you must wrap the above code in <i>another</i>
 * try block in order to catch any exception that may be thrown (including from the call to
 * {@code close()}).
 *
 * <p>
 * This pattern ensures the following:
 *
 * <ul>
 * <li>Each {@code Closeable} resource that is successfully registered will be closed later.
 * <li>If a {@code Throwable} is thrown in the try block, no exceptions that occur when attempting
 * to close resources will be thrown from the finally block. The throwable from the try block will
 * be thrown.
 * <li>If no exceptions or errors were thrown in the try block, the <i>first</i> exception thrown by
 * an attempt to close a resource will be thrown.
 * <li>Any exception caught when attempting to close a resource that is <i>not</i> thrown (because
 * another exception is already being thrown) is <i>suppressed</i>.
 * </ul>
 *
 * <p>
 * An exception that is suppressed is not thrown. The method of suppression used depends on the
 * version of Java the code is running on:
 *
 * <ul>
 * <li><b>Java 7+:</b> Exceptions are suppressed by adding them to the exception that <i>will</i> be
 * thrown using {@code Throwable.addSuppressed(Throwable)}.
 * <li><b>Java 6:</b> Exceptions are suppressed by logging them instead.
 * </ul>
 *
 * @author Colin Decker
 * @since 14.0
 */
// Coffee's for {@link Closer closers} only.
@Beta
@GwtIncompatible
public final class Closer implements Closeable {

    /**
     * The suppressor implementation to use for the current Java version.
     */
    private static final Suppressor SUPPRESSOR =
            SuppressingSuppressor.isAvailable() ? SuppressingSuppressor.INSTANCE : LoggingSuppressor.INSTANCE;

    /**
     * Creates a new {@link Closer}.
     */
    public static Closer create() {
        return new Closer(SUPPRESSOR);
    }

    @VisibleForTesting
    final Suppressor suppressor;

    // only need space for 2 elements in most cases, so try to use the smallest array possible
    private final Deque<Closeable> stack = new ArrayDeque<Closeable>(4);
    private Throwable thrown;

    @VisibleForTesting
    Closer(Suppressor suppressor) {
        this.suppressor = checkNotNull(suppressor); // checkNotNull to satisfy null tests
    }

    /**
     * Registers the given {@code closeable} to be closed when this {@code Closer} is
     * {@linkplain #close closed}.
     *
     * @return the given {@code closeable}
     */
    // close. this word no longer has any meaning to me.
    @CanIgnoreReturnValue
    public <C extends Closeable> C register(@Nullable C closeable) {
        if (closeable != null) {
            stack.addFirst(closeable);
        }

        return closeable;
    }

    /**
     * Stores the given throwable and rethrows it. It will be rethrown as is if it is an
     * {@code IOException}, {@code RuntimeException} or {@code Error}. Otherwise, it will be
     * rethrown wrapped in a {@code RuntimeException}. <b>Note:</b> Be sure to declare all of the
     * checked exception types your try block can throw when calling an overload of this method so
     * as to avoid losing the original exception type.
     *
     * <p>
     * This method always throws, and as such should be called as {@code throw closer.rethrow(e);}
     * to ensure the compiler knows that it will throw.
     *
     * @return this method does not return; it always throws
     * @throws IOException when the given throwable is an IOException
     */
    public RuntimeException rethrow(Throwable e) throws IOException {
        checkNotNull(e);
        thrown = e;
        Throwables.propagateIfPossible(e, IOException.class);
        throw new RuntimeException(e);
    }

    /**
     * Stores the given throwable and rethrows it. It will be rethrown as is if it is an
     * {@code IOException}, {@code RuntimeException}, {@code Error} or a checked exception of the
     * given type. Otherwise, it will be rethrown wrapped in a {@code RuntimeException}.
     * <b>Note:</b> Be sure to declare all of the checked exception types your try block can throw
     * when calling an overload of this method so as to avoid losing the original exception type.
     *
     * <p>
     * This method always throws, and as such should be called as
     * {@code throw closer.rethrow(e, ...);} to ensure the compiler knows that it will throw.
     *
     * @return this method does not return; it always throws
     * @throws IOException when the given throwable is an IOException
     * @throws X when the given throwable is of the declared type X
     */
    public <X extends Exception> RuntimeException rethrow(Throwable e, Class<X> declaredType) throws IOException, X {
        checkNotNull(e);
        thrown = e;
        Throwables.propagateIfPossible(e, IOException.class);
        Throwables.propagateIfPossible(e, declaredType);
        throw new RuntimeException(e);
    }

    /**
     * Stores the given throwable and rethrows it. It will be rethrown as is if it is an
     * {@code IOException}, {@code RuntimeException}, {@code Error} or a checked exception of either
     * of the given types. Otherwise, it will be rethrown wrapped in a {@code RuntimeException}.
     * <b>Note:</b> Be sure to declare all of the checked exception types your try block can throw
     * when calling an overload of this method so as to avoid losing the original exception type.
     *
     * <p>
     * This method always throws, and as such should be called as
     * {@code throw closer.rethrow(e, ...);} to ensure the compiler knows that it will throw.
     *
     * @return this method does not return; it always throws
     * @throws IOException when the given throwable is an IOException
     * @throws X1 when the given throwable is of the declared type X1
     * @throws X2 when the given throwable is of the declared type X2
     */
    public <X1 extends Exception, X2 extends Exception> RuntimeException rethrow(Throwable e, Class<X1> declaredType1,
            Class<X2> declaredType2) throws IOException, X1, X2 {
        checkNotNull(e);
        thrown = e;
        Throwables.propagateIfPossible(e, IOException.class);
        Throwables.propagateIfPossible(e, declaredType1, declaredType2);
        throw new RuntimeException(e);
    }

    /**
     * Closes all {@code Closeable} instances that have been added to this {@code Closer}. If an
     * exception was thrown in the try block and passed to one of the {@code exceptionThrown}
     * methods, any exceptions thrown when attempting to close a closeable will be suppressed.
     * Otherwise, the <i>first</i> exception to be thrown from an attempt to close a closeable will
     * be thrown and any additional exceptions that are thrown after that will be suppressed.
     */
    @Override
    public void close() throws IOException {
        Throwable throwable = thrown;

        // close closeables in LIFO order
        while (!stack.isEmpty()) {
            Closeable closeable = stack.removeFirst();
            try {
                closeable.close();
            } catch (Throwable e) {
                if (throwable == null) {
                    throwable = e;
                } else {
                    suppressor.suppress(closeable, throwable, e);
                }
            }
        }

        if (thrown == null && throwable != null) {
            Throwables.propagateIfPossible(throwable, IOException.class);
            throw new AssertionError(throwable); // not possible
        }
    }

    /**
     * Suppression strategy interface.
     */
    @VisibleForTesting
    interface Suppressor {
        /**
         * Suppresses the given exception ({@code suppressed}) which was thrown when attempting to
         * close the given closeable. {@code thrown} is the exception that is actually being thrown
         * from the method. Implementations of this method should not throw under any circumstances.
         */
        void suppress(Closeable closeable, Throwable thrown, Throwable suppressed);
    }

    /**
     * Suppresses exceptions by logging them.
     */
    @VisibleForTesting
    static final class LoggingSuppressor implements Suppressor {

        static final LoggingSuppressor INSTANCE = new LoggingSuppressor();

        @Override
        public void suppress(Closeable closeable, Throwable thrown, Throwable suppressed) {
            // log to the same place as Closeables
            Closeables.logger.log(Level.WARNING, "Suppressing exception thrown when closing " + closeable, suppressed);
        }
    }

    /**
     * Suppresses exceptions by adding them to the exception that will be thrown using JDK7's
     * addSuppressed(Throwable) mechanism.
     */
    @VisibleForTesting
    static final class SuppressingSuppressor implements Suppressor {

        static final SuppressingSuppressor INSTANCE = new SuppressingSuppressor();

        static boolean isAvailable() {
            return addSuppressed != null;
        }

        static final Method addSuppressed = getAddSuppressed();

        private static Method getAddSuppressed() {
            try {
                return Throwable.class.getMethod("addSuppressed", Throwable.class);
            } catch (Throwable e) {
                return null;
            }
        }

        @Override
        public void suppress(Closeable closeable, Throwable thrown, Throwable suppressed) {
            // ensure no exceptions from addSuppressed
            if (thrown == suppressed) {
                return;
            }
            try {
                addSuppressed.invoke(thrown, suppressed);
            } catch (Throwable e) {
                // if, somehow, IllegalAccessException or another exception is thrown, fall back to
                // logging
                LoggingSuppressor.INSTANCE.suppress(closeable, thrown, suppressed);
            }
        }
    }
}
